The present invention relates to a headlamp apparatus for vehicles such as automobiles for changing the direction of the light-emitting optical axis of a headlamp by making use of a motor as a drive source, and more particularly to a vehicle headlamp apparatus preferred for use for a headlamp apparatus comprising a light distribution control means, such as the Adaptive Front-lighting System (hereinafter, referred to as AFS), for changing the illuminating direction and range of the headlamp to follow the diving direction of a vehicle.
As an AFS that has been proposed to enhance the driving safety of automobiles, U.S. Published Patent Application 2002-0064051 A1 (published on May 30, 2002) describes a technology proposed by the inventor of this invention. As the concept of the technology is briefly shown in FIG. 1, in this AFS, information indicating the driving conditions of an automobile CAR is detected by a sensor 1, and what has been detected is outputted to an electronic control unit (hereinafter, referred to as ECU). As the sensor 1, there are provided, for example, a steering angle sensor 1A for detecting an angle through which a steering wheel SW of the automobile CAR is steered, a vehicle speed sensor 1B for detecting the vehicle speed of the automobile CAR and vehicle height sensors 1C for detecting the respective heights of front and rear axles to detect the horizontality (level) of the automobile CAR (only a sensor for a rear axle is shown in FIG. 1), these sensors 1A, 1B and 1C being connected to the ECU. The ECU 2 controls swivel lamps 3R, 3L or headlamps 3 equipped at the front of the automobile on the right- and left-hand sides thereof, respectively, which are adapted for changing their light distributions by controlling the side-to-side change of the illuminating direction of light based on outputs from the respective sensors 1. As the swivel lamps 3R, 3L, there is provided, for example, a headlamp in which a reflector and a projector lamp that are provided in the headlamp are constructed so as to rotate or swivel in horizontal directions and which comprises a rotationally driving means for rotationally driving the reflector and the projector lamp by means of a drive source such as a driving motor. The mechanism including the rotationally driving means is referred to as an actuator herein. According to the AFS of this type, when the automobile is driven on a curved road, the road surface ahead of a curve on the curved road can be illuminated according to the driving speed of the automobile, and thus, the AFS is effective when attempting to enhance the driving safety of the automobile.
When there occurs in this AFS a defect that the direction of the optical axis of the headlamp cannot be changed properly, that is, when there occurs a defect that the illuminating direction of the headlamp cannot be controlled with the illuminating direction of the headlamp being kept shifted either leftward or rightward relative to the straight-ahead running direction of the automobile, the foreground of the automobile cannot be illuminated when the automobile drives straight ahead or takes a turn at an opposite bend to the direction in which the reflector and the projector lamp are kept shifted, whereby the driving safety is deteriorated. Alternatively, when there occurs a defect that the illuminating direction continues to change side to side, there may be caused a risk that drivers of oncoming vehicles and/or vehicles in the vicinity of the subject vehicle are dazzled and are then put to dangerous conditions. While the following cases are considered as reasons for triggering the defects: there occurs a certain defect in the sensors 1, and no outputs from the sensors 1 cannot be inputted into the ECU 2; there occurs a certain defect in the ECU 2; and there occurs a certain defect in the actuators of the respective swivel lamps 3R, 3L, most of the defects are triggered when a main control circuit such as a microcomputer incorporated in the ECU 2 or sub-control circuits integrally provided on the actuators of the respective swivel lamps 3R, 3L runs away.
When the AFS fails due to the runaway of the main control circuit or the sub-control circuits, since the normal condition can be restored from the failing condition immediately the control circuits are reset, it is considered that a reset circuit is provided on the main control circuit and/or the sub-control circuits. In particular, in case an automatic reset circuit is provided for automatically implementing an automatic reset operation based on a signal which has detected a defect, the control circuit can be reset immediately the defect occurs so as to be recovered from the problematic condition. Since the main control circuit having the ECU 2 can be placed at an appropriate position on the vehicle, as shown in FIG. 1, and there is little limitation imposed on the external size and capacity of the ECU 2, it is relatively easy to incorporate the automatic reset circuit in the main control circuit. However, since the actuator having the sub-control circuit needs to be incorporated in the swivel lamp 3R, 3L, the external configuration and capacity of the actuator are subjected to a certain restriction, and therefore, it is difficult to provide the automatic reset circuit that is provided on the main control circuit on the sub-control circuit. Due to this, once a defect occurs, it becomes difficult to get recovered from a problematic condition quickly by automatically resetting the sub-control circuit.